Studies designed to assess the histomorphological, ultrastructural, histo- chemical and biochemical characteristics of altered cell types in pulmonary neoplasms of mice are currently underway. Over the past year, we have evaluated the gross, histomorphological and ultrastructural characteristics of pulmonary tumors in aged Strain A mice in an attempt to further clarify differences between neoplastic and nonneoplastic lung tissue using conventional light and electron microscopy. Automated lectin staining, two dimensional gel electrophoresis and gold-labeling electron microscopic techniques to evaluate glycoconjugate composition of nonneoplastic versus neoplastic cells, and malignant versus benign tumors, are in progress. Additional studies to characterize the progression of pulmonary neoplasia in other strains of mice including B6C3F1, C3A, C57BL, C3H, B6D2F1 and AC3 utilizing standard morphological and morphometric techniques are underway.